Conventionally, an image forming apparatus which prints images on sheets using toner is put into practical use by an electrophotography. The image forming apparatus includes a heat source unit which heats toner for forming an image, and fixes the image to a sheet by pressurizing the sheet. The heat source unit includes heat rollers, press rollers and the like. The heat source unit heats and pressurizes toner of the image formed on the sheet by conveying the sheet sandwiching the sheet between the heat rollers and the press rollers. A method of, when heating and pressurizing toner, conveying sheets without depositing the melting toner on sheets in the heat source unit of the image forming apparatus is adopted.
Meanwhile, a decoloring device which decolors an image printed on a sheet by the image forming apparatus is being proposed. The decoloring device includes a heat source unit including heat rollers and press rollers similar to, for example, the image forming apparatus. The decoloring device requires a higher amount of heat than that of the image forming apparatus to decolor an image formed on a sheet whose images are repeatedly decolored a plurality of times. The heat source unit of the decoloring device needs to maintain high surface temperatures of the heat rollers to secure the heat amount required for decoloring. By keeping higher temperatures of the heat rollers, the decoloring device can reliably decolor images from sheets whose images are repeatedly decolored a plurality of times. However, when, for example, a sheet on which an image is printed using toner which can be fixed at a lower temperature than a normal temperature passes through the heat source unit of the decoloring device, toner on a sheet surface melts and is offset on surfaces of the heat roller or the press roller. When the melting toner is offset on the heat rollers or the press rollers, the toner is offset from the rollers to a surface of a sheet which passes next through the heat source unit and makes the sheet surface dirty in some cases.